System and method for extracting physiological information from remotely detected electromagnetic radiation

ABSTRACT

The present invention relates to a device and a method for extracting physiological information indicative of at least one health symptom from remotely detected electromagnetic radiation. The device comprises an interface ( 20 ) for receiving a data stream comprising remotely detected image data representing an observed region comprising at least one subject of interest ( 12 ), wherein the image data comprises wavelength-dependent image information, wherein the wavelength-dependent image information is composed of at least two color channels ( 96, 98, 100 ) representative of respective wavelength portions; an image processor ( 22 ) for detecting channel signal strength information for at least two of the at least two color channels ( 96, 98, 100 ); and a data comparison unit ( 24 ) for comparing detected channel signal strengths with respective reference values.

FIELD OF THE INVENTION

The present invention relates to a system and a method for extractingphysiological information indicative of at least one health symptom fromremotely detected electromagnetic radiation. More particularly, thepresent invention may contribute in analyzing vital signs informationindicative of vital parameters, physiological parameters or, moregenerally, health parameters. The electromagnetic radiation may beconsidered as radiation in the visible wavelength band re-emitted by asubject of interest. As used herein, visible radiation may relate toradiation in a particular wavelength range which is visible to a humaneye, or, at least to a sensing device. Even more specifically, thepresent invention may relate to (visible) image capturing and processingsystems and corresponding methods for detecting and monitoring vitalparameters and/or symptom-indicative information which may be applied,for instance, in the field of remote monitoring, such as remotephotoplethysmographic monitoring.

The invention further relates to a corresponding computer program.

BACKGROUND OF THE INVENTION

WO 2011/148280 A1 discloses a device and a method for measuring ananalyte of a subject, the device comprising:

a number of narrow band light sources, each narrow band light sourcebeing structured to emit a spectrum of light covering a number ofwavelengths; and

a number of detector assemblies configured to receive light reflectedfrom a subject, each of the detector assemblies including a filter and aphotodetector, each filter being structured to transmit a maintransmission band and one or more transmission side bands, wherein foreach narrow band light source the spectrum thereof includes one or morewavelengths that fall within the one or more transmission sidebands ofany of the filters.

The document further discloses several refinements of the method and thedevice. For instance, it is suggested to utilize respective lightemitting diodes (LED) as the narrow band light sources. Furthermore, itis envisaged to integrate both the narrow band light sources and thedetector assemblies into a single system and to position the integratedsystem closely to a measurement surface of a subject to be monitored.Eventually, the document seeks after a determination of transcutaneousbilirubin and, based thereon, an estimation of a serum bilirubin level.

While basically avoiding blood sampling for assessing a subject'sphysiological condition or health condition, the device and method of WO2011/148280 A1 may still be considered as an obtrusive approach forsubject monitoring or patient monitoring, at least to a certain extent.The teaching of WO 2011/148280 A1 pertains to the field of contactmeasurement and/or contact monitoring basically requiring to closelyattach sensors, emitters, transducers and further equipment to themonitored subject. This may be experienced as being considerablyunpleasant. Particularly this holds true in the field of neonatalmonitoring or, more generally, infant monitoring.

US 2012/195486 A1 discloses a method of facilitating a first signal foranalysis to characterize at least one periodic component thereof, themethod including obtaining at least two second signals, eachcorresponding to a respective different radiation frequency range, thefirst signal being at least derivable from an output signal obtainableby applying a transformation to the second signals such that any valueof the output signal is based on values from each respective secondsignal at corresponding points in time, obtaining at least one value ofat least one variable determining influences of at least components ofrespective second signals on the output signal when the signalscorresponding to the second signals are captured and the transformationis applied.

WO 2013/038326 A1 discloses a method for extracting information,comprising receiving a data stream comprising a continuous or discretetime-based characteristic signal including physiological information anda disturbing signal portion, the characteristic signal being associatedwith a signal space, the signal space comprising complementary channelsfor representing the characteristic signal, components of thecharacteristic signal being related to respective complementary channelsof the signal space, pre-processing the data stream by splitting arelevant frequency band thereof into at least two defined sub bandscomprising determined portions of the characteristic signal, each ofwhich representing a defined temporal frequency portion potentiallybeing of interest, optimizing the sub bands so as to derive respectiveoptimized sub bands from the at least two sub bands, the optimized subbands being at least partially indicative of a presence of a vitalsignal, and combining the optimized sub bands so as to compose anoptimized processed signal.

US 2012/197137 A1 discloses a method of photoplethysmography, including:processing a signal based on at least one signal from at least onesensor arranged to capture light from a living subject to extractinformation on a characteristic of a periodic biological phenomenon,wherein at least one of the signals from at least one sensor is obtainedby using at least one of a light source and a filter placed before theat least one sensor tuned to a peak in an absorption spectrum of water.

US 2011/157340 A1 discloses a fluorescent imaging device comprising anirradiation section that irradiates an object to be examined withexcitation light and reference light; an image pickup section that picksup a fluorescence image based on the excitation light and a reflectedlight image including a first reflected light image of at least apredetermined wavelength region based on the reference light; an imagesignal generating section that generates a plurality of image signalsmaking up a diagnostic fluorescent image including an image signal of afluorescent image corresponding to the fluorescence image, an imagesignal of the reflected light image including a first reflected lightimage corresponding to the first reflected light image from thereflected light image; a comparison section that compares intensity ofthe fluorescent image and that of the first reflected light imagemultiplied by a predetermined value or relative intensity between thefluorescent image and the first reflected light image; and a selectionsection that selectively outputs one of the first reflected light imageand the fluorescent image based on the comparison result by thecomparison section as one image signal making up the diagnosticfluorescent image.

DE 197 41 982 A1 discloses an apparatus for non-invasive detection ofthe dermal blood perfusion in a measuring area on human limbs,comprising at least one light source that applies light to a measurementarea, wherein the light is reflected from the measurement area and fromunderlying layers; a light detector system that receives the reflectedlight; and a control and evaluation unit to which output signals of thelight detector system are transmitted, wherein an imaging system isprovided that selectively selects a spatial and spectral portion of themeasurement light, thereby imaging the portion of the measuring area onthe light detection system which detects incident light with spatial andtemporal resolution, wherein the imaging system further analyzes imagingsignals, detects and visualizes blood volume changes.

Recently, remote digital image-based monitoring systems for obtainingpatient information or, physiological information of living beings ingeneral, have been described and demonstrated.

As used herein, the term “remotely detected electromagnetic radiation”may refer to radiation components which are sent to a subject ofinterest from a radiation source (such as a remotely positioned lightsource) and “reflected” by a skin portion or dermal portion of thesubject of interest. Also the subject's tissue beneath the skin's topsurface plays a role in the reflection, deflection and/or absorption ofincident radiation. Since reflection mechanisms in the subject's skinare rather complex and multi-dependent on factors such as wavelengths,penetration, depth, skin composition, vascular system structure, andfurther influencing parameters, terms such as “emitted”, “transmitted”and “reflected” shall not be understood in a limited way. Typically, aportion of incident radiation may be reflected at the skin's (upper)surface. Furthermore, a portion of incident radiation may penetrate theskin and pass through skin layers. Eventually, at least a portion of theincident penetrating radiation may be absorbed in the skin, while atleast another portion of incident penetrating radiation may be scatteredin the skin (rather than reflected at the skin's surface). Consequently,radiation components representing the subject of interest which can becaptured by a sensor, particularly an image sensor, can be referred to are-emitted radiation in this context.

For remote monitoring and measurement approaches, the use of cameras hasbeen demonstrated. Cameras may particularly involve video camerascapable of capturing sequences of image frames. Preferably, camerascapable of capturing visible light can be used. These cameras maycomprise a certain responsibility (or: sensitivity) characteristic whichcovers at least a considerable portion of a visible light range of theelectromagnetic spectrum. As used herein, visible light shall beunderstood as part of the electromagnetic spectrum which can be sensedby the human eye without further technical aids.

Remote subject monitoring, e.g., patient monitoring, is consideredbeneficial since in this way unobtrusive non-contact measurements can beconducted. By contrast, non-remote (contact) measurements typicallyrequire sensors and even markers to be applied to a skin portion ofinterest of the subject to be monitored. In many cases, this isconsidered unpleasant, particularly for long-term monitoring.

It would be therefore beneficial to provide for a system and a methodfor remote monitoring which further contribute to overcoming the need ofobtrusive (contact) measurements.

Photoplethysmography (PPG) is an optical measurement technique thatevaluates a time-variant change of light reflectance or transmission ofan area or volume of interest. PPG is based on the principle that bloodabsorbs light stronger than surrounding tissue, so variations in bloodvolume with every heartbeat affect transmission or reflectancecorrespondingly. Besides information about the heart rate, a PPGwaveform can comprise information at reputable further physiologicalphenomena such as respiration.

In this connection, Verkruysse et al., “Remote plethysmographic imagingusing ambient light”, Optics Express, 16(26), 22 Dec. 2008, pp.21434-21445 demonstrates that photoplethysmographic signals can bemeasured remotely with normal ambient light and rather conventionalconsumer level video cameras.

Conventional PPG devices, such as pulse oximeters for measuring theheart rate and the (arterial) blood oxygen saturation (also called SpO2)of a subject are to be attached to the skin of the subject, for instanceto a finger tip, earlobe or forehead. Therefore, they are referred to as“contact” PPG devices.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to seek foradditional applications of PPG systems and corresponding methods.Particularly, it is an object of the present invention to provide asystem and a method for extracting physiological information beingcapable of assisting in assessing health symptoms and contributing todiagnostic routines.

More particularly, it would be advantageous to provide a device and acorresponding method being capable of adequately processing remote PPGinformation without requiring multiple signal transformation steps. Inother words, it would be beneficial to provide a method and a system forextracting physiological information that are particularly adapted toremotely detected image data which generally may comprise enormousdisturbances and noise-affected portions.

In a first aspect of the present invention a remotephotoplethysmographic monitoring system for extracting physiologicalinformation indicative of at least one health symptom from remotelydetected electromagnetic radiation is presented, the system comprising:

an interface for receiving a data stream comprising remotely detectedvideo data representing an observed region comprising at least onesubject of interest, wherein the video data compriseswavelength-dependent image information, wherein the wavelength-dependentimage information is composed of at least two color channelsrepresentative of respective wavelength portions;

an image processor for detecting relative channel signal strengthinformation for at least two of the at least two color channels;

a data comparison unit for comparing detected relative channel signalstrengths with respective reference values obtained from reference datagenerated by monitoring healthy subjects, wherein the data comparisonunit is further configured for determining a ratio of the detectedchannel signal strengths of at least two of the at least two colorchannels and for comparing the ratio of the channel signal strengthswith a reference ratio; and

a symptom analyzer for deriving blood composition-indicative informationfrom the comparison of actual relative channel signal strengths with thereference values.

The present invention is based on the insight that several (health)symptoms occurring in a subject of interest, such as a patient or, moregenerally, a living being or a human being, typically involve acorresponding characteristic change of reflection and/or absorptionproperties at the subject's skin or in the subject's tissue orcirculating blood. Consequently, upon monitoring the subject of interestand generating channel-based (color) image information, slight minutechanges of color strengths or relative color strengths in at least oneof the at least two channels may be highly indicative of respectivehealth conditions or symptoms.

Particularly, the system may focus on relative channel signals strengthinformation. Typically, the received data stream may comprise a PPGsignal having a stable DC component and a relatively small pulsatilecomponent (AC-portion) which may be attributed to the (blood)circulatory system in the subject. Blood pulsation causes slight minutecolor changes in the subject's tissue and/or the skin which may bedetected upon monitoring and capturing respective image information. Inother words, a signal representing the pulsatile component of the atleast two color channels may be presented in a vector space by an indexelement (or: a vector) having a defined length and orientationattributable to actual relative signals strength values in each of theat least two color channels. Due to the blood pulsation, such an indexelement or vector may undergo a more or less periodic “reciprocating”motion between two end positions in the vector space. The path or curveof the reciprocating motion of the index element or vector may be usedas an indicator for the presence of characteristic health symptoms. Asused herein the term “relative signal strength” may relate to signalstrength of an AC signal portion with respect to the (relativelyconstant or mean) DC signal portion of the same color channel.Consequently, an “absolute signal strength” may relate to an absolutesignal strength of a signal incorporating the “constant” DC and the“pulsating” AC portion. The invention makes use of the fact that severalspecific symptoms may involve a characteristic variation in thepulsatile (AC) signal of at least one of the color channels with respectto at least one of the remaining color channels. Given that referencevalues (for instance, representing a healthy subject) for thisreciprocating path or, more generally, for the channel signal strengthsfor at least two of the at least two color channels are available, acharacteristic deviation (in orientation and/or length) from thesereference values may be highly indicative of particular health symptoms,syndromes and/or, more generally, disease patterns.

As used herein, electromagnetic radiation particularly relates tovisible radiation from which visible image information can be obtained.In other words, imaging systems configured for capturing (visible) imagedata are primarily addressed. As mentioned above, visible radiationrefers to radiation portions which may be sensed by the human eye.However, in some embodiments also wavelength portions adjacent to thevisible radiation band may be utilized and detected by a respectivesensing device or capturing device. For instance, also near-infraredradiation, infrared radiation and/or ultraviolet radiation may beutilized. As used herein, the term channel signal strength may basicallyrefer to an intensity and/or an amplitude of detected radiation in arespective wavelength portion assigned to a respective (color) channel.The data stream may comprise information involving blood flow relatedcolor variations at the subject's skin and/or the subject's tissue whereblood flow occurs. As indicated above, primarily a pulsating (AC)portion of the detected image information attributable to the blood flowmay be of interest. As used herein, “remote detection” and/or “remotelydetected” may refer to a monitoring approach or a monitoring arrangementin which a sensing device, such as a camera or a video camera, isarranged at a considerable distance of the to-be-monitored subject. Forexample, the distance between the subject and the sensing device mayinvolve at least several centimeters, but may also involve severaldecimeters or even several meters. Such a remote arrangement allows forfairly unobtrusive measurements. On the other hand, such an arrangementtypically also involves huge disturbances and/or distortion due tounstable illumination conditions and/or motion artifacts related torelative motion between the to-be-monitored subject and the sensingdevice.

The approach presented above is particularly suitable for clinicalhealth monitoring, preferably for neonatal monitoring and/or infantmonitoring. Especially neonates and infants suffer from obtrusivecontact measurement involving fixedly attached sensors and/or markers.According to the above approach, a subject of interest, such as aneonate, may enjoy a certain degree of freedom while still effective andadequate monitoring is ensured.

The data comparison unit may be configured for performing a “polar”comparison (result: greater-than/less-than) of actual values andreference values, determining of a proportion between actual values andreference values, and/or determining an absolute or relative differencebetween actual values and reference values. Actual values may berepresented by detected channel signal strengths. Reference values maybe represented, for instance, by predefined and/or pre-detected channelsignal strengths.

The symptom analyzer makes use of the fact that many diseases and/orhealth distortions in general may affect the subject's bloodcomposition. Changes in the blood composition of the subject may bedetected by comparing actual color information with respective referencecolor information attributed to a healthy subject.

According to another aspect, the at least two color channels areassociated with a color model, the color model being based on a colormodel convention allocating respective wavelength portions to the atleast two color channels. Basically, a color model may providesufficient information allowing for digitization of originally analogousimage information. In other words, under consideration of the colormodel, real colors may be transferred into “bits and bites”.

According to yet another aspect, the color model is color space based ona color space mapping convention, wherein respective wavelength portionsare assigned to respective axes of the color space. Basically the colormodel may provide a mathematical model describing a digitalrepresentation of colors. The color space, however, may be considered asan appropriate color representation based on the respective color model.Such a means may be beneficial since in this way color properties may bepresented by geometric entities, such as vectors, which may facilitatehandling and processing the respective data.

According to yet another aspect, the color space is an additive colorspace composed of three color channels. In this way, based on merelythree different basic colors a great variety of color nuances may be(re)produced. However, in the alternative, basically also subtractivecolor spaces may be utilized. For the sake of illustration, but not in alimiting way, the color space may be an RGB color space. A subtractivecolor space may be a CMY and/or a CMYK color space. In the following,primarily the RGB color model and/or RGB color space is addressed.However, this should not be construed as a limitation. A person skilledin the art may be aware of several alternative and/or substitute colormodels or color spaces. Furthermore, different color models anddifferent color spaces may be transferred into each other.

By way of example, given the exemplary RGB-color space embodiment, ablue to red ratio (B/R) or a red to green and blue ratio (R/(G+B)) maybe indicative of respective health symptoms. Comparing such a ratio witha respective reference ratio may reveal significant deviations. In casea deviation-representative value exceeds a predefined threshold, a clearindication of an occurrence of a symptom may be provided. According to afurther embodiment the symptom analyzer is configured for detecting alevel of serum bilirubin in the subject's circulating blood underconsideration of detected channel strength fluctuations. An increasedlevel of serum bilirubin may be considered as a strong indicator forjaundice. Neonatal jaundice is a yellowing of the skin and other tissuesof a new born infant. Jaundice may also occur among adults. The colorchange is attributed to an increased level of bilirubin. Management andtreatment of jaundiced subjects typically requires assessing andmonitoring the level of serum bilirubin. According to the above aspect,the system may provide for a long-term unobtrusive bilirubinmeasurement. In this way, blood sampling and further obtrusivemeasurement methods can be avoided, at least to a great extend.

According to yet another aspect, the symptom analyzer is configured fordetecting a level of bilirubin accumulated in the subject's dermis underconsideration of detected constant or quasi-constant channel signalstrengths, preferably the symptom analyzer is further configured forderiving an estimate of a serum bilirubin level compared to askin-bilirubin level. This embodiment makes use of the fact thataccumulated bilirubin in the subject's dermis basically alters the DCcomponent of the PPG signal.

In a jaundiced subject, an increased bilirubin level may be present inthe subject's circulating blood. However, due to diffusion, bilirubinmay also accumulate in the subject's skin tissue. Both bilirubinconcentrations in the blood and in the skin may affect the image datafrom which the desired health information may be obtained. It may bethus beneficial to determine and assess an increase of the bilirubinlevel in the blood and an increase of the bilirubin level in the skintissue of the subject. It has been further observed that duringtreatment of jaundice the level of bilirubin in the skin tissue may bereduced faster than the level of bilirubin in the blood. Consequently,the ability of detecting the level of bilirubin in the blood and thelevel of bilirubin in the skin tissue allows for the determination offurther health-indicative values which may be utilized, for instance,for managing and controlling the treatment of jaundice.

According to still another aspect, the symptom analyzer is configuredfor detecting relative channels signal strength information indicativeof impending suffocation. Especially for neonates and infants,suffocation is a great danger which may lead to severe permanentinjuries and even to death. An indication of impending suffocation maybe a ratio of hemoglobin or deoxygenated hemoglobin (HB) to oxygenatedhemoglobin (HBO2) (HB/HBO2). When suffocation is likely to happen, theHB/HBO2 ratio is increased. This may result in a slight color changewhich may be characterized by greater amplitudes in the R-channelcompared to the G-channel and the B-channel in an RGB color space.Therefore, a characteristic orientation change may be detected andutilized for initiating a suffocation alarm. Given that reference valuesare obtained beforehand, suitable threshold values may be predefined.

In this connection it is further preferred if the symptom analyzer isconfigured for assessing oxygenation information under consideration ofa ratio of the detected channel signal strengths, the oxygenationinformation being indicative of a ratio of hemoglobin and oxyhemoglobinin the subject's blood, and for outputting an alert signal when theratio exceeds a reference threshold.

According to a preferred embodiment, the system further comprises animage sensor for remotely recording video data, the image sensorcomprising a responsivity (or: sensitivity) adapted to captureelectromagnetic radiation in at least two wavelength portionscorresponding to the at least two color channels. In this way,consistent image data encoding and processing may be ensured. When thesystem also incorporates the image sensor, such as an RGB-camera, a highlevel of signal integration may be achieved. As indicated above, ratherconventional consumer level video cameras may be utilized. It is evenfurther preferred that the camera, the image processor and furthercomponents of the system basically apply the same color model. Thesensitivity of the image sensor may cover, at least, a considerableportion of visible radiation. However, in some embodiments, thesensitivity of the image sensor may further cover at least a portion ofinfrared radiation and/or ultraviolet radiation.

According to yet another aspect, the system further comprises a patterndetector for detecting at least one indicative skin portion of the atleast one subject of interest.

According to still another embodiment, the system further comprises atreating radiation source for emitting radiation in a particularwavelength range, wherein the treating radiation source is arranged insuch a way that the emitted radiation is directed to the subject ofinterest, preferably the system further comprises a treatment controllerfor operating the treatment radiation source under consideration ofmedical condition-indicative data generated by the data comparison unit.

In other words, the system may also comprise a phototherapy function.Phototherapy may be used for treating jaundice. Particularly, thetreating radiation source may be embodied as a light source capable ofemitting light in the wavelength range of about 400 nm to 500 nm. Inthis way, increased levels of bilirubin in the subject of interest canbe lowered. As indicated above, it is particularly beneficial in thisconnection that the symptom analyzer may be configured for detecting alevel of serum bilirubin in the subject's blood and a level of bilirubinaccumulated in the subject's skin tissue. This information, preferably aratio of a serum bilirubin level to a skin-bilirubin level may beutilized in managing and controlling phototherapy treatment.

In yet another aspect of the present invention, a remotephotoplethysmographic monitoring method for extracting physiologicalinformation indicative of at least one health symptom from remotelydetected electromagnetic radiation is presented, the method comprisingthe steps of:

receiving a data stream comprising video data representing an observedregion comprising at least one subject of interest, wherein the videodata comprises wavelength-dependent image information, wherein thewavelength-dependent image information is composed of at least two colorchannels representative of respective wavelength portions;

detecting relative channel signals strength information for at least twoof the at least two color channels;

comparing detected relative channel signal strengths with respectivereference values obtained from reference data generated by monitoringhealthy subjects, wherein the step of comparing comprises determining aratio of the detected channel signal strengths of at least two of the atleast two color channels and comparing the ratio of the channel signalstrengths with a reference ratio; and

deriving blood composition-indicative information from the comparison ofactual relative channel signal strengths with the reference values.

In yet another aspect of the present invention there is provided acomputer program which comprises program code means for causing acomputer to perform the steps of the method when said computer iscarried out on that computer.

The program code (or: logic) can be encoded in one or morenon-transitory, tangible media for execution by a computing machine,such as a computer. In some exemplary embodiments, the program code maybe downloaded over a network to a persistent memory unit or storage fromanother device or data processing system through computer readablesignal media for use within the system. For instance, program codestored in a computer readable memory unit or storage medium in a serverdata processing system may be downloaded over a network from the serverto the system. The data processing device providing program code may bea server computer, a client computer, or some other device capable ofstoring and transmitting program code.

As used herein, the term “computer” may stand for a large variety ofprocessing devices. In other words, also mobile devices having aconsiderable computing capacity can be referred to as computing devices,even though they provide less processing power resources than standard“computers”. Needless to say, such a “computer” can be part of a medicaldevice and/or system. Furthermore, the term “computer” may also refer toa distributed computing device which may involve or make use ofcomputing capacity provided in a cloud environment. The term “computer”may also relate to medical technology devices, fitness equipmentdevices, and monitoring devices in general, that are capable ofprocessing data.

Preferred embodiments of the disclosure are defined in the dependentclaims. It should be understood that the claimed method and the claimedcomputer program can have similar preferred embodiments as the claimedsystem and as defined in the dependent system claims.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects of the invention will be apparent from andelucidated with reference to the embodiment(s) described hereinafter. Inthe following drawings

FIG. 1 shows a simplified schematic illustration of a system accordingto an embodiment of the present disclosure;

FIG. 2 shows exemplary absorption spectrum charts for hemoglobin and foroxygenated hemoglobin;

FIG. 3 shows an exemplary absorption spectrum chart for bilirubin;

FIG. 4 shows an exemplary diagram indicating spectral sensitivitycharacteristics of a three-channel camera;

FIG. 5 illustrates a schematic illustration of a pulsating PPG signalcomposed of a considerably constant (DC) portion and an overlappingalternating pulsatile (AC) portion;

FIG. 6 illustrates a schematic representation of an exemplary(three-dimensional) color space in which a color vector is present;

FIG. 7 illustrates another representation of the color space accordingto FIG. 6, wherein another color vector is present having a differentorientation and length;

FIG. 8 exemplifies a (two-dimensional) color space in which two colorvectors are presented, wherein also an exemplary path or curve of analternating motion of the pulsating color vector is indicated;

FIG. 9 illustrates a color space in accordance with FIG. 8, whereinanother path or curve of the alternating motion of the pulsating colorvector is illustrated having a different length and orientation whencompared with the path or curve illustrated in FIG. 8;

FIG. 10 illustrates relative blood pulsation-related amplitudes for aset of reference subjects in three respective wavelength portions orcolor channels;

FIG. 11 illustrates a to-be monitored subject, wherein an indicativeskin portion is highlighted from which a mean PPG general may beobtained;

FIG. 12 shows a simplified schematic illustration of a system accordingto an alternative embodiment of the present disclosure; and

FIG. 13 shows an illustrative block diagram representing several stepsof an embodiment of a method in accordance with the present disclosure.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a schematic illustration of a set-up of a system 10 inaccordance with an embodiment of the present invention. By way ofexample, but not to be understood in a limiting way, the system 10 maybe used in neonatal care units for monitoring a subject 12 such as aneonate or infant. In general, the system 10 may be configured formonitoring subjects 12 such as patients or, more generally, human beingsor living beings. Especially neonates may be positioned on a lyingsurface 14 which may be part of a hospital bed or an arrangementspecifically adapted for receiving and supporting newborn infants, suchas an incubator.

Neonatal jaundice (also known as hyperbilirubinemia) often occurs amongnewborns since the neonate's liver might be underdeveloped at the verybeginning and therefore not able to excrete and, consequently, reducethe level of bilirubin. So-called unconjugated bilirubin may be formedas a degradation by-product during the destruction of old red bloodcells. Since the neonate's organism may not be capable of efficientlyabsorb and reduce bilirubin, unconjugated bilirubin levels often raisein newborns. When a level of unconjugated bilirubin rises beyond a givenbinding capacity, unconjugated bilirubin may diffuse out of thecirculatory system and enter neighboring tissues. Typically, thediffusion of free bilirubin into the subject's 12 skin tissue may causea characteristic yellowing of the skin tone. Especially for prematureneonates, increased bilirubin levels may even lead to severe braindysfunction, for instance to kernicterus. Since the liver function andthe circulatory system in general is less developed among prematureneonates they face a higher risk of severely suffering from increasedbilirubin levels.

Since conventional approaches for measuring and monitoring the bilirubinlevels in the subject 12 often have been experienced as being unpleasantand obtrusive, some embodiments of the present invention seek forproviding reliable and unobtrusive monitoring techniques which may evenenable long-term monitoring. To this end, the system 10 may comprise adata processing device 16 which may be coupled with or incorporate asensor or camera 18. Since the system 10 is configured for processingimage data, such as video data, the sensor 18 may be embodied by arather conventional video camera, for instance. Fairly unobtrusivemeasurement may be achieved since the camera 18 may be arranged at adistance from the subject 12 to be monitored. In other words, accordingto preferred embodiments of the present disclosure, the sensor 18 doesnot have to be embodied by contact sensors to be attached to thesubject's skin. For instance, the sensor 18 may incorporate a CCD-arrayor a CMOS-array for sensing and digitizing image information, such asvisible radiation and, in some embodiments, infrared radiation and/orultraviolet radiation. In this context, the term visible radiation mayalso refer to radiation portions that are primarily “visible” to thesensor 18. The camera 18 may be connected with an image processor 22 viaan interface 20. Via the interface 20, image data may be transmitted tothe image processor 22. Preferably, the camera 18 is configured fordecomposing and transferring analogous image information into digitalimage information comprising at least two color channels.

For instance, the camera 18 may be arranged as a video camera capable ofcapturing and generating RGB-image data. Image data, such as RGB-imagedata may be processed accordingly by the image processor 22. Forinstance, the image processor 22 can be configured for detecting(relative) channel signals strength information for at least some,preferably for all of the color channels the image data is composed of.As indicated above, characteristic channel signal strengths or channelsignal strength ratios may be highly indicative of physical conditionsor, more specifically, health conditions, of the subject 12. The dataprocessing device 16 may further comprise a pattern detector 23 fordetecting at least one indicative skin portion of the at least onesubject of interest 12. As known in the art, the pattern detector 23 mayutilize skin detection algorithms so as to distinguish between(indicative) skin portions and (non-indicative) surrounding portionswhich also may be present in the image data.

The image processor 22 is basically configured for condensing thedigital image information into dimension-reduced (relative) strengthinformation. To this end, the image processor 22 may be capable oftransferring a plurality of image entities (or: pixels) into a singleentity representing a respective pattern, wherein the single entity iscomposed of basically two or more values indicating respective colorchannel signal strengths. In other words, the desired informationcontained in a two-dimensional (colored) pixel pattern may beagglomerated and transferred into a single index element or color vectorcharacterized by a length and an orientation. The length and theorientation of the color vector are attributable to respective signalstrengths at at least some of the color channels.

Preferably, the image processor 22 is further configured for providingfor image data normalization. For instance, time-based normalization canbe applied to captured image data. Given the exemplary embodimentimplementing R (red), G (green) and B (blue) channels, the imageprocessor 22 may be configured for dividing their actual values by arespective time-average value. The time-average value for each of thechannels may be based on a running average over a window having apredefined size. Alternatively, the time-average value may be based onan average over a time-interval, wherein all samples (each actual value)in a specified time-interval may be divided by the same average overthat interval. In this way, a variation in the strength and/or color ofany illumination device illuminating the subject 12 may be sufficientlyattenuated so as to avoid and/or reduce disturbing influences.

A data stream comprising the channel signal strength informationdetected by the image processor 22 may be delivered to a data comparisonunit 24 for comparing the detected channel signal strengths withrespective reference values. In other words, the data comparison unit 24may be configured for assessing characteristic differences of thechannel signal strengths with respect to reference values (e.g., interms of length and/or orientation). As indicated above, characteristicdeviations in length and/or in orientation may be highly indicative ofparticular health symptoms. For comparing the data and/or for assessingdifferences, the data comparison unit 24 may be provided with referencedata from which the reference values may be obtained. Reference data maybe generated, for instance, upon monitoring healthy subjects 12.

Based on characteristic deviations, the presence of characteristicsymptoms may be assessed. However, the data processing device 16 mayfurther comprise, in the alternative or in addition, a symptom analyzer26 for deriving blood composition-indicative information from acomparison of actual (relative) signal strengths with the referencevalues. So the symptom analyzer 26 can make use of the fact that manycharacteristic symptoms may involve variances or changes of the bloodcomposition of the subject 12 which may find expression in slight colorchanges and/or deviations of the AC portion of the PPG signal which maybe detected by the system 10. As indicated above, slight color changesoccurring in the patient's blood and/or skin tissue may be attributed,for instance, to an increased level of bilirubin and/or may be a strongindicator for an impending suffocation incident. At least one of thedata comparison unit 24 and the symptom analyzer 26 may be furtherconfigured to provide output data which may be used for further analysesand/or for display measures.

The output data may be provided at the output interface 28. Furthermore,at least one of the data comparison unit 24 or the symptom analyzer 26can be adapted for generating an alert signal which may be submitted toa respective alert signal interface 30 which may be coupled with analert unit 32. Especially when severe symptoms are detected, the alertunit 32 may be triggered so as to generate an alert signal for alarmingthe subject 12, medical staff or, more generally, care taking personsabout severe deviations detected by the system 10. Consequently, countermeasures may be taken accordingly.

The data processing device 16 may be further coupled with a monitoringradiation source 38. The monitoring radiation source 38 may be embodiedby a light source arranged for illuminating a portion of theto-be-monitored subject 12 which is observed by the camera 18.Consequently, relatively stable illumination conditions may be achievedcontributing to noise reduction and/or disturbance minimization. Themonitoring radiation source 38 may be embodied by a conventional lightsource emitting light in a particular wide wavelength range, preferablyadapted to the sensitivity of the camera 18. Also the monitoringradiation source 38 may be controlled and/or managed by the dataprocessing device 16. To this end, the monitoring radiation source 38may be connected via an interface 36 to a monitoring light controller34. The monitoring light controller 34 may be coupled with at least oneof the image processor 22, the data comparison unit 24 and the symptomanalyzer 26. In doing so, the data processing device 16 may be providedwith illumination information facilitating (image) data processing.

According to some exemplary embodiments, the data processing device 16may be further coupled with a treating radiation source 44. This appliesin particular when the system 10 is further configured for providingphototherapy. Phototherapy may be a suitable treatment for increasedbilirubin concentrations in the subject 12, especially for neonates.Phototherapy treatment may typically involve at least one light source44 capable of emitting light in the wavelength range of about 400 toabout 500 nm. The light directed at the subject's 12 skin may interactwith the accumulated bilirubin in the subject's 12 skin tissue. In thisway, the bilirubin level may be sufficiently decreased over time.Preferably, also the treating radiation source 44 is connected to thedata processing device 16. For instance, the treating radiation source44 may be connected via an interface 42 with a treatment controller 40.The treatment controller 40 may be connected to at least one of theimage processor 22, the data comparison unit 24 or the symptom analyzer26. Provided that an increased level of bilirubin is detected by thedata processing device 16, the treating radiation source 44 may becontrolled so as to selectively emit radiation to the to-be-treatedsubject 12. On the other hand, being aware of actual phototherapytreatment, the data processing device 16 may consider this informationwhen processing the respective data. As indicated above, phototherapymay efficiently decrease the level of bilirubin in the skin tissue ofthe subject 12. However, typically the serum bilirubin level in thesubject's blood may not be reduced accordingly at the same time. Havingknowledge of phototherapy treatment taking place allows for assessing aserum bilirubin concentration more precisely.

The image processor 22, the data comparison unit 24 (and, if provided,any of the symptom analyzer 26, the monitoring light controller 34 andthe treatment controller 40) may be implemented by a common processingunit, such as the data processing device 16, which can be considered asa computing device, or at least, part of a computing device driven byrespective logic commands (program code) so as to provide for desireddata processing. The data processing device 16 may further compriseseveral components or units which may be addressed in the following. Itshould be understood that each component or unit of the data processingdevice 16 may comprise a number of processors, such as multi-coreprocessors or single-core processors. At least one processor can beutilized by the data processing device 16. Each of the processors can beconfigured as a standard processor (e.g. central processing unit) or asa special purpose processor (e.g. graphics processor). Hence, the dataprocessing device 16 can be suitably operated so as to distributeseveral tasks of data processing to adequate processors.

The data processing device 16 as well as at least one of the interfaces20, 28, 30, 36, 42 can be embodied in a common processing apparatus orhousing. Basically, the imaging unit or camera 18 and the monitoringradiation source 38 (and, if any, the treating radiation source 44) aregenerally external elements, but may also be integrated into a commonhousing with the data processing device 16. Furthermore, each of theimage processor 22, the data comparison unit 24, and the symptomanalyzer 26, the monitoring light controller 34 and the treatmentcontroller 40 may be implemented by hardware means or by software means.Also a hybrid implementation including hardware and software componentsmay be envisaged.

FIG. 2 and FIG. 3 illustrate exemplary absorption spectra diagrams forblood (including hemoglobin and oxygenated hemoglobin) and forbilirubin. In each of the diagrams, an axis of abscissas indicated byreference number 52 represents a respective wavelength interval coveringa range between about 250 nm and 750 nm. An ordinate axis 50 representsa (qualitative) absorption behavior of the respective materials. In FIG.2, a graph representing the absorption spectrum for oxygenatedhemoglobin (HBO2) is indicated by reference number 54. A graphrepresenting the absorption spectrum of (deoxygenated) hemoglobin (HB)is indicated by reference number 56. As can be clearly seen, enrichmentof hemoglobin with oxygen slightly shifts a respective absorption peak.Based on this phenomenon, for instance, impending suffocation may bedetected since accordingly basically a level of (deoxygenated)hemoglobin rises while a level of oxygenated hemoglobin decreases. Thismay result in slight color variations, compared with a healthy subject.Assuming that the system 10 is configured for operating on the basis ofan RGB color space, the above variation may result in greaterpulsatility in the R-channel when compared to the G- and B-channels.Therefore, a corresponding slight orientation change of a color vectorin the RGB color space may be detected.

FIG. 3 illustrates an absorption spectrum of bilirubin wherein arespective graph is indicated by reference number 58. When the level ofbilirubin in the monitored subject 12 is increased, the characteristicbilirubin absorption pattern may influence detected channel signalstrengths accordingly. For instance, a respective RGB signal may beshifted to an increased pulsation amplitude in the B-color channel andto a moderately increased pulsation amplitude in the G-channels whilethe pulsation amplitude in the R-channel may be decreased. Also thisvariation may result in a characteristic orientation change of the colorvector in the color space.

In other words, according to the above aspects, the present disclosuremay aim at a “mediate” qualitative detection of abnormal healthconditions. Provided that reference data characterizing healthy subjectscan be obtained beforehand, potentially dangerous health conditions suchas jaundice and/or starting suffocation may be reliably detected duringlong term monitoring.

FIG. 4 illustrates a diagram indicating a spectral responsivitycharacteristic of an exemplary sensor or camera 18. An axis of abscissas64 may stand for a particular wavelength while an ordinate axis 62represents a corresponding sensitivity. A graph 66 represents anR-channel. A graph 68 represents a G-channel. A graph 70 represents aB-channel. In total, the graphs 66, 68, 70 may cover a visible lightspectral portion visible to the human eye. Given that for each of thechannels R, G, B respective input signals are separately captured andstored by the camera 18 respective corresponding data values or entitiesallow for a color representation in the RGB color space. Consequently,multi-channel color information may be represented by a color vector ina respective multi-dimensional color space.

FIG. 5 illustrates a representation of an exemplary PPG signal indicatedby reference numeral 78 over time. An axis of abscissas 76 representstime. An ordinate axis 74 basically represents a signal strength.Typically, the PPG signal 78 is composed of a relatively large constantportion or DC portion, refer to reference number 80. Furthermore, thePPG signal 78 is characterized by a relatively small pulsating oralternating portion 82. The pulsations in the alternating portion or ACportion 82 may be attributed to blood pulsation in the subject 12.However, further information can be obtained from the AC portion 82. Theoverall PPG signal 78 illustrated in FIG. 5 may be composed of aplurality of color channels. Consequently, the representation providedin FIG. 5 may involve a dimensional reduction, for the sake ofillustration. In other words, each value or entity of the PPG graph 78may be composed of two or more components, for instance of respectiveR-values, G-values and B-values.

FIG. 6 and FIG. 7 illustrate a three-dimensional representation of amulti-channel color space 86. Each of the color spaces 86 may representabsolute PPG signals (including the DC and the AC portion) or relativePPG signals (including the AC portion). For the sake of simplicity, thecolor space 86 may be referred to as an RGB-color space composed of anR-channel (reference number 88), a G-channel (reference number 90), anda B-channel (reference number 92). FIG. 6 further illustrates an indexelement or color vector 94. The color vector 94 may be athree-dimensional vector having three respective components. Forinstance, the color vector 94 may be composed of component vectors 96,98, 100 assigned to respective axis or channels 88, 90, 92. A pulsationor alternating variation of the PPG signal 78 (reference number 82 inFIG. 5) may involve a corresponding alternating characteristic variation(in terms of orientation and length) of the color vector 94 over time.In this connection, FIG. 7 illustrates another color vector 102. For thesake of simplicity, the color vectors 94 and 102 may represent oppositeextreme values (minima and maxima) of the alternating pulsating portion82 of the PPG signal 78 in FIG. 5. Over time, due to blood pulsation anactual color vector may be alternatingly moved along a path between the“boundary color” color vectors 94 and 104.

Such a relative color variation is indicated by reference number 104 inFIG. 8. FIG. 8 and FIG. 9 represent simplified two-dimensional colorspaces 86 a. Particularly for illustration purposes, the color spaces 86a are merely composed of two color channels 88, 90. In FIG. 8 two colorvectors 94 a, 94 b are present which may represent extreme values of thepulsating PPG signal component. Reference number 104 indicates aresulting relative color path or curve. The relative color path 104typically may have a curved shape. However, for the sake of simplicity,the relative color path 104 in FIG. 8 basically comprises a straightline. For instance, the relative color path 104 may represent areference color path of blood flow induced pulsations for a healthysubject 12. The color path 104 may be characterized by a givenorientation and length. The relative color path 104 may also bedescribed by respective pairs of values 98 a, 96 a and 98 b, 96 bindicating respective signals strength at the first color channel 88 andthe second color channel 90.

The relative color path 104 representing a healthy subject is indicatedin FIG. 9 by a dashed double arrow. Furthermore, a deviating relativecolor path or curve 106 is presented in FIG. 9. The relative color path106 may represent a subject 12 suffering from jaundice or impendingsuffocation. Further symptoms may be detected upon monitoring andinvestigating characteristic deviations in a present relative color pathin a monitored subject 12. Needless to say, the desired deviation to bedetected may also be obtained through monitoring the color vectors 94 a,94 b as such. A comparison of signal strengths or relative signalstrengths for at least some of the at least two color channels 88, 90may also result in highly indicative values.

FIG. 10 shows an illustrative diagram indicating components of a bloodpulsation-indicative PPG signals for a data set over 105 exemplary(healthy) subjects with different skin types. On an axis of abscissas112 the respective number of the individuals is denoted, wherein theskin tone of the subjects ranges from very light on the left side tovery dark on the right side. An ordinate axis 110 indicates aqualitative relative signal strength in the respective channels R, G, B.Reference number 115 indicates a red color channel (R), reference number118 indicates a blue color channel (B) and reference number 116indicates a green color channel (G). Despite several outliers, thedetected signal also referred as blood volume pulse (or: Pbv) isremarkably stable.

The main chromophores (or: colorants) for light with a wavelengthbetween 400 and 950 nm in healthy human skin are melanin and blood. Theblood is contained in the vascular system and only the arterial partexhibits the pulsation leading to the color variation over time. Themelanin is concentrated in the epidermis which consequently acts as afilter between the dermis, including blood vessels, and any camera andlight source. Since the blood volume pulse may be measured in anormalized color space (e.g., actual values divided by time-averagevalues), the effect of the filtering may be removed in the normalizeddata and, consequently, the skin-type has no major influence on theorientation of the blood volume pulse or the respective color vector.

It is therefore concluded that a corresponding orientation of the PPGsignal vector (see the color vectors 94, 102 in FIGS. 6 through 9) maybe utilized as a considerably robust health indicator for symptoms ofseveral diseases and/or health conditions which may affect at least oneof the skin color (or: skin-tissue color) or the color of the pulsatingblood. Typically, both the skin color and the blood color may beaffected. Again referring to FIG. 10, it is concluded that for subjectshaving dark skin a relative signal strength in the blue channel may bedecreased while the relative signal strength in the red channel may beincreased. This effect may be attributed to specular reflection which islikely to occur among subjects having dark skin. However, this influencemay be observed and compensated accordingly. For further improvingmonitoring accuracy respective reference values may be chosen so as toreflect the subject's 12 preconditions on a personal level. This mayeven involve providing further contextual information describing theto-be-monitored subject 12. Contextual information may relate to theobserved skin color tone and, if any, the duration and/or intensity ofphototherapy, for instance. Furthermore, known health issues the subject12 is facing may be provided beforehand so as to further improve theresponse accuracy or detection accuracy of the system.

Referring to FIG. 11, another exemplary illustration of ato-be-monitored subject 12 is provided. When monitoring the subject 12,the sensor or video camera 18 (FIG. 1) may be controlled and/or adjustedso as to basically monitor an indicative skin portion 120 of the subject12. The system 10, particularly the data processing device 16, may befurther configured for applying pixel pattern-based motion compensationor, more generally, spatial signal normalization to the detected andcaptured video data. An area of interest of the subject 12 in FIG. 11 ismasked with an exemplary pixel pattern 122. The pixel pattern 122 maycover both basically indicative portions of the subject 12 and basicallynon-indicative portions. When agglomerating respective signal pixelvalues of the pixel pattern 122, a mean pixel value can be derived whichis denoted by reference number 124 in FIG. 11. In this way, amulti-dimension video signal may be transferred into acolor-representative signal basically composed of a single entity. Inthis way, undesired motion of the subject 12 can be compensated or, atleast, attenuated in the resulting mean color signal 124.

FIG. 12 shows an alternative arrangement of a system 10 a for extractingphysiological information indicative of at least one health symptom fromremotely detected electromagnetic radiation. Particularly, analternative data processing device 16 a is schematically illustrated inFIG. 12. As to their basic set-up both the data processing device 16illustrated in FIG. 1 and the data processing device 16 b illustrated inFIG. 12 may be similarly configured. The data processing device 16 a mayfurther comprise a memory unit or storage 126 which may also be referredto as reference memory unit or storage. The reference memory unit orstorage 126 may be configured for storing reference values representingexpected channel signals strength in the color channels the input videodata is basically composed of which are attributed to healthy subjects12. In this way, a set of reference values may be provided based onwhich occurring deviations (including orientation and/or length changes)may be detected and assessed accordingly. The reference memory unit orstorage 126 may be connected to at least one of the data comparison unit24 or the symptom analyzer 26. The reference memory unit or storage 126may be further connected to a respective interface 128 where input datamay be received.

The data processing device 16 a may further comprise a calibration inputmemory unit or storage 130. The calibration input memory unit or storage130 may be configured for storing further calibration informationintended for use at the personal level of the to-be-monitored subject12. To this end, for instance, contextual information may be providedvia an interface 132. Consequently, the reference memory unit or storage126 may comprise overall basic reference information while thecalibration input memory unit or storage 130 may comprise furtherpersonal calibration information. Also the calibration input memory unitor storage 130 may be connected to at least one of the data comparisonunit 24 and the symptom analyzer 26. The memories or storages 126, 130can take the form of (real) hardware memories or (virtual) softwarememories. Particularly, the memories or storages 126, 130 can beembodied by the same memory element.

FIG. 13 schematically illustrates a method for extracting physiologicalinformation indicative of at least one health symptom from remotelydetected electromagnetic radiation. At a first step 150, the method anda related process may be initiated. A step 152 may follow whichcomprises remotely capturing an image data stream comprising image datarepresenting an observed region comprising at least one to-be-monitoredsubject of interest. In a further step 154, the image data stream may bereceived by a data processing device. The image data stream may bebasically composed of multi-channel image data, such as three-channelcolor image data. For instance, RGB-image data may be transferred to thedata processing device. In yet another step 156, channel signal strengthinformation may be detected for each of the plurality of color channels.The step 156 may further include the detection of relative channelsignal strength information. A further step 158 may follow comprising acomparison of detected channel signal strengths or relative channelsignal strengths with respective reference values. Another step 160 mayfollow which may comprise analyzing detected variations and/ordeviations so as to eventually assign or attribute characteristicdeviations to corresponding health symptoms. At a further step 162, themethod may terminate. Needless to say, the method may be used in acontinuous monitoring process, such as a long-term monitoring process.Of course, also short-term or spot check monitoring may be envisaged.

By way of example, the present invention can be applied in the field ofhealth care, e.g. unobtrusive remote patient monitoring, generalsurveillances, security monitoring and so-called lifestyle environments,such as fitness equipment, or the like. Applications may includemonitoring of oxygen saturation (pulse oximetry), heart rate, bloodpressure, cardiac output, changes of blood perfusion, assessment ofautonomic functions, and detection of peripheral vascular diseases.Needless to say, in an embodiment of the method in accordance with theinvention, several of the steps described herein can be carried out inchanged order, or even concurrently. Further, some of the steps could beskipped as well without departing from the scope of the invention.

In the claims, the word “comprising” does not exclude other elements orsteps, and the indefinite article “a” or “an” does not exclude aplurality. A single element or other unit may fulfill the functions ofseveral items recited in the claims. The mere fact that certain measuresare recited in mutually different dependent claims does not indicatethat a combination of these measures cannot be used to advantage.

A computer program may be stored/distributed on a suitable(non-transitory) medium, such as an optical storage medium or asolid-state medium supplied together with or as part of other hardware,but may also be distributed in other forms, such as via the Internet orother wired or wireless telecommunication systems. Furthermore, thedifferent embodiments can take the form of a computer program productaccessible from a computer usable or computer readable medium providingprogram code for use by or in connection with a computer or any deviceor system that executes instructions. For the purposes of thisdisclosure, a computer usable or computer readable medium can generallybe any tangible apparatus that can contain, store, communicate,propagate, or transport the program for use by or in connection with theinstruction execution device.

Furthermore, the different embodiments can take the form of a computerprogram product accessible from a computer usable or computer readablemedium providing program code for use by or in connection with acomputer or any device or system that executes instructions. For thepurposes of this disclosure, a computer usable or computer readablemedium can generally be any tangible device or apparatus that cancontain, store, communicate, propagate, or transport the program for useby or in connection with the instruction execution device.

In so far as embodiments of the disclosure have been described as beingimplemented, at least in part, by software-controlled data processingdevices, it will be appreciated that the non-transitory machine-readablemedium carrying such software, such as an optical disk, a magnetic disk,semiconductor memory or the like, is also considered to represent anembodiment of the present disclosure.

The computer usable or computer readable medium can be, for example,without limitation, an electronic, magnetic, optical, electromagnetic,infrared, or semiconductor system, or a propagation medium. Non-limitingexamples of a computer readable medium include a semiconductor or solidstate memory, magnetic tape, a removable computer diskette, a randomaccess memory (RAM), a read-only memory (ROM), a rigid magnetic disk,and an optical disk. Optical disks may include compact disk-read onlymemory (CD-ROM), compact disk-read/write (CD-R/W), and DVD.

Further, a computer usable or computer readable medium may contain orstore a computer readable or usable program code such that when thecomputer readable or usable program code is executed on a computer, theexecution of this computer readable or usable program code causes thecomputer to transmit another computer readable or usable program codeover a communications link. This communications link may use a mediumthat is, for example, without limitation, physical or wireless.

A data processing system or device suitable for storing and/or executingcomputer readable or computer usable program code will include one ormore processors coupled directly or indirectly to memory elementsthrough a communications fabric, such as a system bus. The memoryelements may include local memory employed during actual execution ofthe program code, bulk storage, and cache memories, which providetemporary storage of at least some computer readable or computer usableprogram code to reduce the number of times code may be retrieved frombulk storage during execution of the code.

Input/output, or I/O devices, can be coupled to the system eitherdirectly or through intervening I/O controllers. These devices mayinclude, for example, without limitation, keyboards, touch screendisplays, and pointing devices. Different communications adapters mayalso be coupled to the system to enable the data processing system tobecome coupled to other data processing systems, remote printers, orstorage devices through intervening private or public networks.Non-limiting examples are modems and network adapters and are just a fewof the currently available types of communications adapters.

The description of the different illustrative embodiments has beenpresented for purposes of illustration and description and is notintended to be exhaustive or limited to the embodiments in the formdisclosed. Many modifications and variations will be apparent to thoseof ordinary skill in the art. Further, different illustrativeembodiments may provide different advantages as compared to otherillustrative embodiments. The embodiment or embodiments selected arechosen and described in order to best explain the principles of theembodiments, the practical application, and to enable others of ordinaryskill in the art to understand the disclosure for various embodimentswith various modifications as are suited to the particular usecontemplated. Other variations to the disclosed embodiments can beunderstood and effected by those skilled in the art in practicing theclaimed invention, from a study of the drawings, the disclosure, and theappended claims.

Any reference signs in the claims should not be construed as limitingthe scope.

1. Remote photoplethysmographic monitoring system for extractingphysiological information indicative of at least one health symptom fromremotely detected electromagnetic radiation, comprising: an interfacefor receiving a data stream comprising remotely detected video datarepresenting an observed region comprising at least one subject ofinterest, wherein the video data comprises wavelength-dependent imageinformation, wherein the wavelength-dependent image information iscomposed of at least two color channels representative of respectivewavelength portions; an image processor for detecting relative channelsignal strength information for at least two of the at least two colorchannels; and a data comparison unit for comparing detected relativechannel signal strengths with respective reference values obtained fromreference data generated by monitoring healthy subjects, wherein thedata comparison unit is further configured for determining a ratio ofthe detected relative channel signal strengths of at least two of the atleast two color channels and for comparing the ratio of the relativechannel signal strengths with a reference ratio; and a symptom analyzerfor deriving blood composition-indicative information from thecomparison of actual relative channel signal strengths with thereference values.
 2. System as claimed in claim 1, wherein the at leasttwo color channels are associated with a color model, the color modelbeing based on a color model convention allocating respective wavelengthportions to the at least two color channels.
 3. System as claimed inclaim 2, wherein the color model is a color space based on a color spacemapping convention, wherein respective wavelength portions are assignedto respective axes of the color space.
 4. System as claimed in claim 3,wherein the color space is an additive color space composed of threecolor channels.
 5. System as claimed in claim 1, wherein the symptomanalyzer is configured for detecting a level of serum bilirubin in thesubject's circulating blood under consideration of detected signalstrength fluctuations.
 6. System as claimed in claim 1, wherein thesymptom analyzer is configured for detecting a level of bilirubinaccumulated in the subject's dermis under consideration of detectedconstant or quasi-constant channel signal strengths, preferably thesymptom analyzer is further configured for deriving an estimate of aserum bilirubin level compared to a skin-bilirubin level.
 7. System asclaimed in claim 1, wherein the symptom analyzer is configured fordetecting relative channel signal strength information indicative ofimpending suffocation.
 8. System as claimed in claim 7, wherein thesymptom analyzer is further configured for assessing oxygenationinformation under consideration of a ratio of the detected channelsignal strengths, the oxygenation information being indicative of aratio of hemoglobin and oxyhemoglobin in the subject's blood, and foroutputting an alert signal when the ratio exceeds a reference threshold.9. System as claimed in claim 1, further comprising: an image sensor forremotely recording video data, the image sensor comprising aresponsivity adapted to capture electromagnetic radiation in at leasttwo wavelength portions corresponding to the at least two colorchannels.
 10. System as claimed in claim 1, further comprising: apattern detector for detecting at least one indicative skin portion ofthe at least one subject of interest.
 11. System as claimed in claim 1,further comprising: a treating radiation source for emitting radiationin a particular wavelength range, wherein the treating radiation sourceis arranged in such a way that the emitted radiation is directed to thesubject of interest, preferably the system further comprises a treatmentcontroller for operating the treating radiation source underconsideration of medical condition-indicative data generated by the datacomparison unit.
 12. Remote photoplethysmographic monitoring method forextracting physiological information indicative of at least one healthsymptom from remotely detected electromagnetic radiation, comprising thesteps of: receiving a data stream comprising video data representing anobserved region comprising at least one subject of interest, wherein thevideo data comprises wavelength-dependent image information, wherein thewavelength-dependent image information is composed of at least two colorchannels representative of respective wavelength portions; detectingrelative channel signal strength information for at least two of the atleast two color channels; and comparing detected relative channel signalstrengths with respective reference values obtained from reference datagenerated by monitoring healthy subjects, wherein the step of comparingcomprises determining a ratio of the detected relative channel signalstrengths of at least two of the at least two color channels andcomparing the ratio of the relative channel signal strengths with areference ratio; and deriving blood composition-indicative informationfrom the comparison of actual relative channel signal strengths with thereference values.
 13. Computer program comprising program code means forcausing a computer to carry out the steps of the method as claimed inclaim 12 when said computer program is carried out on the computer.